The present invention relates to the art of induction heating and, more particularly, to a method and apparatus for inductively heating and quench hardening small bores of workpieces.
The invention is particularly applicable for inductively heating a small internal splined bore of a workpiece preparatory to quench hardening thereof and it will be described with particular reference thereto; however, the invention has many broader applications and may be useful for inductively heating various small workpiece passages.
In the field of heat treating, inductively heating a cylindrical surface of a workpiece to an elevated temperature and subsequently quenching it, is a well accepted technique for providing locally hardened surfaces. Therein a multi-coiled inductor is energized by a high frequency power supply so as to be magnetically coupled with the adjacent surface of a workpiece. The resultant induced flux inductively heats the surface to the desired depth and heat treating temperature such that the subsequent quenching produces the requisite quench hardening of the surface.
In order for such hardening to be effective, the inductor must be able to transfer the requisite flux to the workpiece surface in order to raise the temperature to the required level. For outer cylindrical surfaces and larger diameter inner cylindrical surfaces, the inductor coil can be sized to effectively transfer the necessary flux energy. In cases of small internal diameters, however, the size of the coil is limited, and for small diameters of an inch or less it has not heretofore been possible to use induction heating to provide localized case hardening of these internal surfaces. In applications such as internally splined hubs and the like, alternative heat treating to inductive case hardening is necessary. These alternatives are more expensive and do not provide the localized hardening which induction heating can provide.